Signal generator including current control element and signal forming element for achieving low noise level and low switching loss

A signal generator for use in driving current through a load, comprising:

• a current control element for controlling a current flowing through an electric load, wherein the current control element is disposed between a direct current power supply and the electric load;
• and
• a signal forming element for outputting a control signal to the current control element, wherein
• the signal forming element generates the control signal in such a manner that the current flowing through the electric load has a rising edge and a down edge of a substantially sine waveform,
• the rising edge of the current is disposed at a timing when the current control element is switched on, and
• the down edge of the current is disposed at a timing when the current control element is switched off,
• wherein
• the signal forming element includes approximate-waveform forming means and a low pass filter,
• the approximate-waveform forming means generates and outputs the control signal, which has a predetermined waveform of a broken line approximation,
• the low pass filter filters a low frequency part of the control signal,
• the approximate-waveform forming means includes a capacitor,
• the capacitor is charged in a case where the control signal is in a rising edge period so that increase degree of a terminal voltage of the capacitor is switched with a plurality of steps,
• the capacitor is discharged in a case where the control signal is in a down edge period so that decrease degree of the terminal voltage of the capacitor is switched with a plurality of steps, and
• the approximate-waveform forming means generates the control signal by switching the increase degree and the decrease degree of the terminal voltage with a plurality of steps.